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CHEST Outstanding Educational Activity Award
The France Foundation was the winner of the Clinical Resource Center Outstanding Educational Activity Award in Professional Development at the 2009 American College of CHEST Physicians Annual Meeting.
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Paul W. Noble, MD, ChairpersonKevin R. Flaherty, MD
Jeffrey A. Golden, MD
Kevin O. Leslie, MD
Steven D. Nathan, MD
Maria L. Padilla, MD
Glenn D. Rosen, MD
Steven A. Sahn, MD
W. Richard Webb, MD
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Article Summary
Swigris JJ, Wamboldt FS, Behr J, et al. The 6 minute walk in idiopathic pulmonary fibrosis: longitudinal changes and minimum important difference. Thorax. 2010;65:173-177.
Introduction:
The 6 minute walk test (6MWT) is gaining increasing recognition as a simple test for following the course of patients with IPF. It provides a functional assessment as well as important prognostic information. It also has a role as an endpoint for clinical studies of therapeutic interventions in IPF. There is inherent variability to the 6MWT and what constitutes a minimum important difference (MID) in IPF has not been well studied. The objective of this study was to establish the MID of the 6MWT by mining the data from a completed prospective drug trial that included the collection of serial 6MWTs, pulmonary function data, and quality of life measurements.
Methods:
Data from 154 patients who participated in a completed prospective, double-blind, randomized, placebo-controlled trial of bosentan (BUILD-1) were used for this study. Among the criteria for inclusion in BUILD-1 were:
- A baseline 6MWT distance of between 150-499 meters
- An FVC between 50-90% of predicted
- A DLCO > 30% of predicted
6MWTs were performed in all patients at baseline 6 months and one year. In the present analysis, 2 methods were used to establish the 6MWT MID:
- Anchor-based method, where the MID is calculated based on changes in another well-established parameter (which is itself sensitive to change). The two anchors chosen were the FVC and the St. George's Respiratory Questionnaire (SGRQ) total score
- Distribution-based method using the estimated effect size
Results:
The calculated MID varied from 10.8 meters (anchor-based against a SGRQ change of 5-10 points at 6 months) to 58.5 meters (Distribution-based method at 6-12 months). The grand mean of all the estimates of the MID was 28 meters.
Expert Opinion:
The 6MWT is being used increasingly to follow IPF patients in the clinic as well as an endpoint for clinical trials in IPF. This paper is important as it provides some guidance as to what should be regarded as a significant change. There are a few caveats to this study. First, as the authors point out, the 28 meter change derived from this dataset might only be useful at the population level and not necessarily for individual patients. This change might be much less than what might be clinically important for an individual patient. Additionally, the conclusions of this study might not be applicable to all patients with IPF because it was based on the subset of patients meeting the BUILD-1 inclusion criteria. Nonetheless, this paper does provide important information and insight into the interpretation of serial changes in the 6MWT distance in patients with IPF.
Additional References
- Caminati A, Bianchi A, Cassandro R, Mirenda MR, Harari S. Walking distance on 6-MWT is a prognostic factor in idiopathic pulmonary fibrosis. Respir Med. 2009;103(1):117-123.
- Holland AE, Hill CJ, Conron M, Munro P, McDonald CF. Small changes in six-minute walk distance are important in diffuse parenchymal lung disease. Respir Med. 2009;103(10):1430-1435.
- Eaton T, Young P, Milne D, Wells AU. Six-minute walk, maximal exercise tests: reproducibility in fibrotic interstitial pneumonia. Am J Respir Crit Care Med. 2005;171(10):1150-1157.
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